1. Field of the Invention
The present invention relates to a guide unit equipped on a transport mechanism of a machine tool and so forth that guides an object to be moved with high accuracy, and more particularly, to a guide unit that improves dust resistance by blocking the openings of fastening member insertion holes formed in a track rail. In addition, the present invention relates to a track rail unit combining a top cover that covers said fastening member insertion holes and said track rail. Moreover, the present invention relates to said top cover itself.
2. Description of the Prior Art
An example of this type of guide unit of the prior art is a linear motion rolling guide unit shown in FIGS. 1 through 3.
As shown in the drawings, said linear motion rolling guide unit is composed of track rail 1, in which tracks in the form of a pair of track grooves 1a are formed in both the right and left sides along the lengthwise direction, a slider in the form of slide unit 3 having rolling element circulating path 2 (refer to FIGS. 1 and 2; to be described in detail hereinafter) and able to move relative to said track rail 1, and a large number of rolling elements in the form of balls 4, that bear the load between track rail 1 and slide unit 3 by circulating while rolling over the above-mentioned track grooves 1a accompanying movement of slide unit 3, and which are arranged and contained within said rolling element circulating path 2.
The above-mentioned slide unit 3 has casing 6, a pair of end caps 7a and 7b coupled to both ends in the direction of progress of said casing 6, and two seals 8a and 8b attached to the outer surfaces of each of said end caps 7a and 7b. Grease nipple 9 for supplying grease to the above-mentioned balls 4 is attached to one end cap 7a.
As shown in FIG. 2, the above-mentioned rolling element circulating path 2 is composed of a load bearing track in the form of load bearing track groove 2a and return path 2b formed linearly and mutually in parallel in the above-mentioned casing 6, and a pair of roughly semi-circular direction changing paths 2c and 2d which are formed in both end caps 7a and 7b and connect said load bearing track groove 2a and return path 2b at both of their ends. Furthermore, said load bearing track groove 2a corresponds to track groove 1a of track rail 1.
The linear motion rolling guide unit having the above-mentioned constitution is arranged on, for example, a bed equipped on, for example, a machine tool in the form of flat bed 10 (shown in FIG. 3), and track rail 1 is fastened to said bed 10 with a plurality of fastening members in the form of bolts 12 (with hexagon sockets). More specifically, as shown in FIGS. 1 and 3, insertion holes are arranged in a row in the lengthwise direction of track rail 1 such that countersunk portions 1c, having a diameter larger than the heads of said bolts 12, and holes 1d, having a diameter slightly larger than the threaded portions of bolts 12, are mutually concentric, and bolts 12 are inserted and screwed into bed 10 so that their entirety is embedded in said countersunk portions 1c and holes 1d. In addition, as shown in FIGS. 1 and 3, disk-shaped plugs 15 for blocking the openings of the insertion holes are fit onto countersunk portions 1c. The outside surface 15a of this plug 15 is formed to be flat, and lies in the same plane as top surface 1e of track rail 1.
In the linear motion rolling guide unit having the above-mentioned constitution, a table for holding a workpiece (not shown) is bolted to slide unit 3, and this operates as the moving side. Namely, in the state in which a workpiece is placed on said table, said table is, for example, reciprocated by a driving device not shown, and accompanying this reciprocating movement, prescribed work, and more specifically cutting processing, is performed on said workpiece. Furthermore, as shown in FIG. 1, a plurality of threaded holes 6a are formed in the upper surface of casing 6 equipped on slide unit 3, and the above-mentioned table is fastened to said casing by bolts (not shown) that screw into these threaded holes 6a.
In the above-mentioned linear motion rolling guide unit, seals 8a and 8b act to wipe off dust and so forth on track rail 1 during sliding of slide unit 3. In addition, since the openings of insertion holes formed in track rail 1 for insertion of bolts 12 are blocked by plugs 15, retention of dust and so forth in these insertion holes is prevented, and is removed by seals 8a and 8b.
Although said linear motion rolling guide unit has this type of dust prevention function, it is not always easy to perfectly position outside surfaces 15a of the above-mentioned plugs 15 (see FIG. 3) to be in the same plane as top surface 1e of track rail 1. In addition, plugs 15 are gradually pushed down during the time operation of slide unit 3 continues. Thus, it is difficult to reliably avoid the retention of dust and so forth on plugs 15, and the entry of dust into slide unit 3 that slides over said plugs 15 cannot be avoided. In the case dust and so forth enters slide unit 3, together with the risk of damage to the above-mentioned balls 4, rolling element circulating path 2 and track surfaces 1a, the service life of said linear motion rolling guide unit is shortened.
The linear motion rolling guide unit shown in FIGS. 4 and 5 as a second example of the prior art is able to eliminate these problems. Furthermore, said linear motion rolling guide unit is disclosed in Japanese Patent Laid-Open Publication No. 5-16043.
As shown in the drawings, in this linear motion rolling guide unit, since a track rail in the form of linear guide rail 101 is fastened to installation surface 102, rail attachment holes 101a formed in said linear guide rail 101 for insertion of bolts 103, namely insertion holes, are covered by a top cover in the form of rail plate 105. Said rail plate 105 extends along the lengthwise direction of linear guide rail 101, and is mounted on said linear guide rail 101.
The following indicates the constitution of mounting rail plate 105 to linear guide rail 101.
First, fitting groove 101b is formed in the top of linear guide rail 101 along its lengthwise direction, and rail plate 105 fits into this fitting groove 101b. Said rail plate 105 and fitting groove 101b have a roughly trapezoidal shape with respect to the perpendicular cross-section in the lengthwise direction. As a result, rail plate 105 is prevented from coming out in the upward direction.
In addition, rail plate 105 is mounted on linear guide rail 101 by hook piece 107 and screw 108 at both ends in its lengthwise direction. More specifically, locking hole 105a and indented locking edge 105b are formed on both ends of rail plate 105, and hook edge 107a is hooked on said locking edge 105b by hook piece 107 having said hook edge 107a and an L-shaped cross-section, and fastened to the end of linear guide rail 101 by screw 108.
As a result of providing the above-mentioned rail plate 105, the rail upper surface over which a slider in the form of linear slider 110 slides is made completely smooth. For this reason, dust and so forth that has fallen onto or adhered to said rail upper surface is reliably removed by scraper 111 provided on both ends in the direction of progress of said linear slider 110, thus preventing entry into said linear slider 110. This type of constitution is preferably used in machinery operating in environments particularly in which there is generation of large amounts of dust and so forth, such as machine tools (cutting machines, grinding machines, etc.), woodworking machines and cutters. Furthermore, examples of dust and so forth include metal cuttings represented by iron and alumina cuttings, and wood chips and so forth produced during woodworking.
Since the above-mentioned rail plate 105 is mounted on linear guide rail 101 in the above-mentioned linear motion rolling guide unit, while fitting groove 101b is formed having a trapezoidal cross-section in said linear guide rail 101, hook piece 107 and screw 108 are used as fasteners. Moreover, a female threaded portion for screwing in this screw 108 is formed in the end of linear guide rail 101.
Thus, in the case of this constitution in which a long groove and female threaded portion are formed in the guide rail itself while also requiring the use of fasteners, the number of steps required for processing and assembly becomes large and the scale of the processing work is also large, thus inviting increased costs. In addition, according to the above-mentioned constitution, in the case of fabricating linear motion rolling guide units of various lengths, various rail plates each having the above-mentioned locking hole 105a and locking edge 105b must be made available corresponding to each of the end positions of these linear guide rails of different lengths, thus resulting in the problem of an increase in the number of processing steps making it difficult to reduce costs.
In addition, in the case it becomes necessary to replace the above-mentioned rail plate 105 as a result of being damaged by some cause, together with having to remove each of the above-mentioned fasteners, rail plate 105 must be pulled out in the lengthwise direction from fitting groove 101b of linear guide rail 101 (since it cannot be lifted out due to the roughly trapezoidal shape of its cross-section), after which a new one must be installed by following the reverse procedure. Thus, a considerable amount of processing steps are required during replacement, and this replacement work is bothersome for a worker.
In addition, since the above-mentioned rail plate 105 and linear guide rail 101 are mutually fit together, they cannot be treated as individual products, thus making it difficult to use only rail plate 105 for other types of guide rails in which this fitting groove portion is not formed.